In order to study the effect of blood flow shear stress on endothelial cells(ECs),we established a simple parallel flow chamber system,which can produce048dyn/cm 2 steady laminar flow shear stress.Using this system,the effect of shear stress on F-actin,G-actin and the morphology of ECs were studied.The results shows under12,24,48dyn/cm 2 shear stress for12h the stress fiber (F-actin)which aligned originally in its own long axis gradually become along the direction of blood flow.The contents of F-actin increased and the contents of G-actin decreased.The morphology of ECs have no changes.It demonstrated that the simple parallel flow cham-ber system is useful in assessing the effects of shear stress on ECs .